Is database normalization still necessary?
It depends on what type of application(s) are using the database.
For OLTP apps (principally data entry, with many INSERTs, UPDATEs and DELETES, along with SELECTs), normalized is generally a good thing.
For OLAP and reporting apps, normalization is not helpful. SELECT queries will run much more quickly against a denormalized schema, which could be achieved with views.
You might also find some helpful information in these very popular similar questions:
Should I normalize my DB or not?
In terms of databases, is “Normalize for correctness, denormalize for performance” a right mantra?
What is the resource impact from normalizing a database?
NoSQL is not a silver bullet: it is simply a technology that may provide a far better fit for for certain circumstances. For relationally-shaped data, the RDBMS is not going away any time soon.
yes, for a transactional system always normalise, or chances are you're going to have major headaches further down the road. For a database that will be used for reporting/OLAP denormalising the schema can be very helpful.